Răspuns :
a + b = 27
a = b + 7
b + 7 + b = 27
2b = 27 - 7
2b = 20
b = 20 : 2
b = 10
a = 10 + 7
a = 17
a = b + 7
b + 7 + b = 27
2b = 27 - 7
2b = 20
b = 20 : 2
b = 10
a = 10 + 7
a = 17